Hardware · Topic 9 of 13
BIOS and UEFI Firmware Settings
Learn what BIOS and UEFI firmware do, how POST and boot order work, and settings such as Secure Boot, TPM, passwords, virtualization and updates.
- 4 min
- POST tests the hardware; beep codes or messages report faults.
- UEFI replaces BIOS, supports GPT, large drives and Secure Boot.
- Boot order decides which device the firmware tries first.
What it is
Firmware is the small program stored on a motherboard chip. It starts the hardware, tests it and then hands control to the operating system.
The older form is the basic input/output system (BIOS). The modern form is the Unified Extensible Firmware Interface (UEFI). Both have a setup screen where a technician changes settings.
How it works
POST and boot
When the computer starts, the firmware runs the power on self test (POST). It checks the processor, memory and basic devices.
Errors show as beep codes or messages. The firmware then looks for a boot device in the boot order and loads the operating system from it.
BIOS compared with UEFI
| Feature | BIOS | UEFI |
|---|---|---|
| Interface | Text menus, keyboard only | Often graphical, mouse support |
| Disk partition style | Master boot record (MBR) | GUID partition table (GPT) as well |
| Boot speed | Slower | Faster |
| Security | Basic passwords | Adds Secure Boot |
| Large drives | Limited to about 2 terabytes (TB) per boot disk | Supports very large boot disks |
Many UEFI boards still have a compatibility mode that behaves like BIOS for old operating systems. The globally unique identifier (GUID) partition table is the newer layout that UEFI uses.
Entering setup
You enter the setup screen by pressing a key during start up, such as Delete, F2, F10 or Esc. The key is shown on screen or in the manual. After changing a setting, save and exit, or the change is lost.
Key settings
| Setting | What it does |
|---|---|
| Boot order | The sequence of devices that firmware checks for an operating system |
| Secure Boot | Allows only trusted, signed boot software, which blocks some malware |
| Trusted Platform Module (TPM) | A chip that stores keys and supports disk encryption and trusted start up |
| Supervisor (admin) password | Needed to change firmware settings |
| User password | Needed to start the computer |
| Virtualization | Turns on processor support for virtual machines |
| Fan and temperature | Shows temperatures and sets fan speed |
| Universal Serial Bus (USB) ports | Can turn off front or unused ports, or block boot from USB |
| Date and time | Sets the clock; wrong time may mean a dead battery in the complementary metal oxide semiconductor (CMOS) memory circuit |
A hardware security module (HSM) is a separate device or card that stores and uses cryptographic keys. A TPM is a smaller chip fixed to the board with a similar goal.
Boot password and lock down
A supervisor password stops others from changing boot order or turning off Secure Boot. Removing a boot device from the list, or turning off USB boot, prevents someone from starting another operating system from a USB drive.
If a computer ignores a bootable USB drive, check the boot order and whether Secure Boot or USB boot is blocking it.
Updating firmware
Makers release firmware updates to fix bugs, add CPU support and close security flaws. The update, often called flashing, writes new code to the chip.
Do not turn the computer off during a flash. A power failure at that moment can leave the board unusable. Use a stable power source, and on a laptop plug in the charger.
Resetting settings
If a bad setting stops the computer starting, you can reset the firmware to its defaults from the setup screen. If you cannot enter setup, clear the CMOS using a jumper on the board or by removing the CMOS battery for a short time, with the power unplugged. A failed battery causes the clock and settings to reset every time.
What to remember for the exam
- POST tests the hardware; beep codes or messages report faults.
- UEFI replaces BIOS, supports GPT, large drives and Secure Boot.
- Boot order decides which device the firmware tries first.
- Secure Boot allows only trusted boot software.
- A TPM stores keys and supports encryption; an HSM is a separate key device.
- A supervisor password protects settings; a user password protects start up.
- Virtualization support may need to be enabled in firmware.
- A flash updates firmware and must not be interrupted.
Common mistakes
Forgetting to save. Changes in setup apply only if you save and exit.
Interrupting a firmware update. A power loss during the flash can render the board unusable.
Changing boot mode on an installed system. Switching between legacy and UEFI mode can stop an existing installation from starting.
Assuming a lost password is easy to remove. A firmware password may need a reset procedure from the maker.
Mixing up TPM and Secure Boot. A TPM stores keys; Secure Boot checks that boot software is trusted.
Check yourself
What does POST do?
It tests the CPU, memory and basic devices when the computer starts, and reports problems by beeps or messages.
Which firmware setting stops unsigned boot software from loading?
Secure Boot.
What is a common sign of a dead CMOS battery?
The date, time or firmware settings reset every time the computer starts.
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